In a typical fixed wireless access system each subscriber is provided with a subscriber transceiver system which is located at the subscriber's premises and which is in radio communication with a radio base station which it shares with other subscribers in the locality. In the Nortel Fixed Wireless Access (FWA) system, the transmit and receive bands between the subscriber transceiver systems and the base station are in the 3.5 GHz region. Typically the system may utilise one or more base stations arranged on a cellular frequency re-use planning basis, and the base stations may be connected to the local exchange by a standard 2 Mbit/s G703 link using the V5.2 or other concentrating interface standards. However it will be appreciated that other systems may be used, for example channel-associated signalling (CAS) systems.
The number of subscribers per base station can range from typically up to 75 in a sparsely populated rural area to around 3000 in a densely populated urban area, depending on how many transceivers are provided at the base station. In a typical tri-sector arrangement, each sector is capable of providing sixty voice calls or thirty data calls. The voice calls may be coded using a 32 kbit/s ADPCM (Adaptive Differential Pulse Code Modulation) coding scheme, whereas the data may be coded using a 64 kbit/s PCM A-Law or μ-law coding scheme. This is found to give excellent voice quality and data transfer at very acceptable rates.
However, with the phenomenal increase in the use of data services and internet applications such as web browsing, the typical usage of the line by the subscriber has changed enormously. Originally telephone lines and communications links with local exchanges (central offices) were primarily designed to handle voice traffic of relatively short holding times typically of an average of about three minutes. An internet call consists of data traffic and a typical holding time can be about thirty minutes or considerably longer. This can create a problem in fixed wireless access systems and indeed other more conventional telephone networks, both because of the extended length of these calls and due to the fact that they can effectively occupy two potential voice lines, and so there is a real likelihood of blocking at peak times. Also, many Internet service providers have a point of presence at the local exchange and so these extended calls are charged at local rate only.